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. C. S. GORDON ET AL V REDUCTION OF ATTENUATION DUE TO THE CONDUCTANCE LOSSES IN cnoss ARMS AND INSULATOR PINS Oct. 16, 1928.

2 Sheets-Sheet 1 Filed July 1, 19 5 AAAIIAA AAAAAA INVENTORS aSfiordom ffl Jl'liau/e ATTORNEY Oct. 16, 1928.

v 1,687,556 AL- CONDUCTANCB TOR PINS 2 She C. 5. G0 N OF A LOSSES IN RDON ET ION DUE TO RMS AND July 1, 1

HE INSULA 925 TTENUAT CROSS A Filed REDUCTIO ets-Sheet 2 INVENTORS GJZGordonfiJTlowe BY i 6 ATI'ORNE;

Patented Get. 16, 1928.

UNITED STATES PATENT OFFICE.

CHESTER S. GORDON, OF NEW YORK, N. Y., AND JAMES T. LOWE, NEWARK, NEW

JERSEY, ASSIGNORS TO AMERICAN TELEPHONE PORATION OF NEW YORK.

REDUCTION OF ATTENUATION DUE TO THE CONDUCTANCE LOSSES IN CROSS ARM INSULATQR PINS.

Application filed. July 1, 1925. Serial No. 40,895.

This invention relates to transmission circuits, and more particularly to means for and methods of reducing the transmission loss in such circuits. 1

With the development of methods of transmitting telephonic and telegraphic signals by means of carrier currents propagated along open Wire lines, new transmission problems have been introduced. Owing to the .fact that the carrier'currents einployedare'relatively high infrequency as compared with the voice currents or Morse currents utilized in the ordinary methods of, communication, it has been found that the attenuation is very markedly increased, so much so,.iii fact, that repeaters for amplifying the transmitted currents-must be separated by much shorter distances, thereby adding .to the expense of the plant" outside the-terminal: stations 'at which the-carrier apparatus is applied. Furthermore, the attenuation is sogreat that it has been impractical'to employ' on telephone lines carrier frequencies much above 30,000 cycles Per second;

An 'analysisof the factors; producing this attenuation shows that there .are' threeqprincipal factors entering into'it j first, the A. C. resistance of the line conductors themselves, which -increases with frequency; because. of the skin effect; second, a leakage-loss in .the

insulators, employed; ;an,d,1 third, z;an;.additional leakage loss in-thecross-arms and p ns carrying the insulators.

At presentthere are no p-ractical ineth ods' of eliminating the losses .due to the first of these factors, as this loss appears to be inherent in the conductor itselfa's now constructed.

The losses due to the second of these factors, sometimes referredto as the hysteresis losses in the material of the insulator,may be to a large extent overcome by certain improved methods of insulator construction which form no part of the present invention." The third factor may be eliminated'by' short-cirtuiting the cross-arms and insulator pins,

that is. by connecting a conductor of substantially no resistance, from the inner surface of one insulator to the inner surface of a corresponding insulator. The object of the present invention is. to provide a simple, economical and efficient means for establishing such connections.

The nv n ion may now be more fully on sulator derstood from the following description when read in connection with the accompanying drawing, in which Figure 1 illustrates the normalarrangementof the cross-arms and insulator pins of a transmission line; F igl 2 is an equivalent electricalcircuit for the arrangement of Fig. 1; F ig..3 illustrates the mannerin which the cross-arms and in pins may be s'hort-circuit'ed; Fig. 4 is an equivalent electrical circuit forthe. arrangementof F ig.. 3 ;.F igs'. 5 and 6 are theoretical circuits illustrating the factors that enter into the propagation of alternatingcurrents along'transinission lines; F ig. 7 'is a series of curvesillustrating the reduction in transmissionloss due to short circuiting the ;cross.arms"and insulator pins; Fig. 8 shows the-form;in which apiece of metal may be AND TELEGRAPH COMPANY, A COR- S AND stamped! out-in the preliminary operation of constructing. a metallic thimble to .be placed over aximsulator pin -in carrying out, the

.present invention Fig. 9 is a cross-section of the "elements shownfin F ig;

trates the two;completedethiinblesaand the connecting conductor; Fig. 11 is a sectional 8;. Fig. 10 illusview showi'nm-the formation of the threads ofthe' e; :;Fig."12-:illustrat -es aj typical i insulatorzpin uponwwhich thethi'mbleris to beiplaceii; Fig. 13shows' the; insulator: adapt Fed-to be-mountedonthe pin after the thin:-

blis' in position ;'iFig.- 14 shows the thimble with aimodified form of conducting strip adapted tolbeusedrin connection with crossarms at which transpositions-are 'made; and Fig. 15 is apcrspective view showinghowthe short'cilcliiting? nnections are established ata-transpositlonpoint. r

Before describing-the detailed st-ructure by .whi'ch insulator pins-andv cross-arms may be: short-circuited in accordance :with the present invention, a brief discussion of the causes of ;transmission lossin open vire lines Iwill be given. Referring to Fig. 1, wl1ich illustrates in simplified form a. typical cross-arm ar-.

rangement such as is employed in connection with telephone lines,

1 and Qdesignatesa pair of conductorsof a telephone line such as are commonly strung from pole to pole across the country in ordinary open-wire construction. The cross-arm 3 is usually a wooden bar hav. ing wooden pins 4 and 5 upon which are mounted insulators 6 and 7, usually of glass or other non-Conductive material. The c nd o tors l and Q'are secured to the insulators 6 and 7 by means of tie wires or conductors 8 and 9. In order to understand how the losses arise from leakage through'such a system as that abo e described it must be remembered that the wood comprising the cross-arm 3 and the pins fl and 5 is not a pertect non conductor but is in fact a relatively pooi-'die l ectr ic as compared with the glass of which the insulators (3 and 7 are composed. Thecross-arm and the pins therefore act as a condenser with a shunt leakage path of high resistance. Furthermore the metal of the conductors-1 and 2 adjacent'to the insulators and the metal of the tie wires 8 and 9-constitute a plate. of a con denser of which the glass insulator itself is the dielectric and of which the-wooden-pin is the other plate. During wet weather-conditions the outer-plate of the condenser. is in eii'ezt, considerably enlarged in area due to the wetting of the outer surface ofthe glass-of the insulator, so that the leakage eifectsproduced by the insulator are greatly augmentediin wet weather. f't

The action of the insulator .andits associated parts as a condenser involves three factors-first, the capacityC, between its'plates (that is, the capacity between the:line-conductor, tie wire and moisture, if any,-on' iits outer surface, on the one hand, and theinsulator pin, on the other-'handz); second, the conductance G representing thedirect cur- 4 rent leakage from the-line conductor over the outer surface of the insulator and un der its pettieoat to the supporting-pin, This direct current leakage does not'var y with=frequenuy, and being surface-leakage, us, of course,

worse in wetweathe'r than in dry weather, but even at its worst represents a; rather, small element of=the total transmission loss ;ithird,

the conductance-G whichi represents thedL electric hysteresis losses in the material ot'the insulator itself. This conductance is a function of the capacity of I the-insulato'r and increases with the frequency, 50 that at hjigh frequencies it becomes a very material factor.

These elements entering into the-action of the insulator are illustrated indiagrammatic form in Fig. 2. Over and above these factors there are two other factors with which the present invention is primarily concerned, namely, the equivalent capacity C of the cross-arm and pins, and the equivalent con (luctance Gut, representing the sum of the true conductance between the inner surface of one insulator and that of the other, and an additional conductance representingthe dielectric losses in the cross-arm and pins.

These factors are also represented schematicface of the insulator 7.

-inherent in the 'mater ial. oi

ally in Fig. 2. In order to eliminate the equivalent conductance of the pins and the cross-arm, in accordance with the present invention the wooden pin is sheathed by a thimble. of conductiye material and the thimbles of corresponding insulators are directiy connected together bya metallic con- .dnctonschematically represented at 10 in Fig. 3, said conductor being of substantially Zero resistance st that practically a dead shortcircuit connection exists between the inner surface ofthc insulator 6 andthe inner sur- The resultant equivalent electrical circuit is illustrated diagrammatically in Fig. 4.

The present invention thus far in the description has been limited to a circuitof a single pair of wires, It is obviously applicable to circuits consisting of several wires. For example, the common hantom' circuit employs two wires in each si e-ot the circuit. For such a circuit the metallic pins in one case or the metallic-sheathsinthe other case are all joined by a metallic conductor so that a substantially short circuit connection exists between the inner-surface of all insulators of the one side of the circuit and the inner surface of all insulators of the other side.

In order to understand how this construction result-5' in reducing the leakage loss. in-

'olving, as it does, an arrangement'which at first thought would seem to provide a better leakage path than the ori inalconstruction, a brief discussion of the't eory of transmission will now be considered. Re-ferring'to I Fig; 5. any transmission'system of the usual type herein discusscd maybethought of as-fa linema'de-upbf a-large-number of sections,eachrsectionfcompiisihg series inductance I); due to theina terial of the line wires themselves. series resistanceR, which is also the line wires themselves,'a shunt capacity C; and a shunt conductance G. The propagation constantof such aconducti e system may be expressed by thewell-known formula:

which 2] is the propagation constant per unit lengtlnand R, L, G and C are, respectively, the resistance, inductance, conductance, andcapacit-y per unit length. I m is: times the frequency; 7' is the operator J 1; I1 is the attenuation constant per unit length, and 6 is a termrepresenting a mere change in the phase of the current transmitted. Now the value of a in the above equation is given by the expression:

,(l LE is large compared to R", and

no no? C m is large compared with G, which is in turn mounted upon;pins carried by crossthe case for the frequencies employed for carrier transmission, the expression reduces to? aeR/2Jo L+G/2"-'/L o It therefore followsthat any reduction of either the resistance R- orthe conductance G will result in a decrease in the attenuation of the circuit.

As has already been stated, the resistance R, being an inherent characteristic of the line conductors themselves, cannot be eliminated by any practical physical means. It is, however, possible to effect a very large reduction in'the conductance G.

In order to apply the theoretical considerations just disclosed to the practical problem presented in the case of open-wire lines car ried upon poles, let us refer to the diagram of Fig. 6 which shows the electrical. equivalent of an open-wire line whose conductors are mounted upon glass.insulatorswhich are arms. The capacity; C-oiFimb-isnow represented by the capacity 0,; due to the air acting as aidielcetric between the line conductors,-.and the capacitiesQand C, which correspond'to the capacitiesdue to the ution of-an insulator as =acondenser, as already described.- Theiaction ofithe air asa dielectric involves no leakageloss, or, at any rate, the leakage loss is' so small that'it may be neglectcd.- -The capacities CU-and Q how..

ever, have' associate'd with them dielectric losses.representedby: the conductances G and G Likewise; the eonduct ances 'G and G are associated; with; these, capacities, but these conductances'.represent direct..cur-

value. As already stated, how eyen gill iof the conductancesassociated n nth the capacican be approximated'in practice. =For. this condition it is clear that the current flowing through the conductance G will produce an energy loss which, of course, must be subtracted from the energy transmitted along the circuit. If this-conductance is short-circuited, however, the current flowingbetween wires is a pure capacity current which pro duccs no loss. In this connection it may be i at all ireq'uericies.

rent: leakageionly andl gllez of relatiyely small noted that the result which applicant attains by shortircuit-ing the pins and cross-arm could theoretically beobtained by making their equivalent conductance zero, but it is impossible to'realize this condition in practice; l

An idea of the magnitude of the reduction inle'aka e loss thus effected ma be obtained fromconsideration of the curves of Fig.7. These curves represent the attenuation at different frequenciesof. a transmission line, each of the curves representing a different condition of the circuit. The curve A, for example, represents the variation of attennation with frequency where the transmission line involves series resistance R (the skin effect), series inductancc'L, and shunt capacity C, butno leakage conductance G; It will be observed that the attenuation increases as the frequency becomes higher, and

this jis ,due'to the fact that the series resist ance Basmvolvedblf there were no ser es resistance, the atte nation would be uniform Curjn'z 15' represents the variaj ron inattenuation .with' frequency, as obseryed in 1 an actual; transmission lineunder dry' weather con-- dition Here,' of course, w'e"'h'ave" leakage 'conduct'an'ceG' due to the hyfs'teresis loss in the ins ilators gafiaidueto the leakage through ,the cro 'ssgarnijaiid piiisz' -"Cur've' Qisa similar curve for same circuit under wet weather Conditions. ltfwill be'oliserved'that the athas now been-enormouslyincreased,

i pnmaiuy to the, wettingof thesurfaceof P ere

\ insulators; thereby increasing the caty with j a consequent increase of the dipeeled for the Weizmann" condition: when tlieattenuatipn enormously increased. Not rniist the circuit be so arranged'that the be commercial under this 'cfe'nd'it on, bu'tj speciail"arrangements must be pro'yidedi forfmairitaining theitransinission 'derfall" weather conditions'." It becomespbyiousi therefore, thatifthe enormousloss represented'by'thecurve C can be eliminated "or even substantially eliminated ,soth'atwe have a; condition approaching the curve A, an iinn'ien'sef saving in the plant will be effected not'only by reason of the reduction in the numberof repeaters necessary, but alsobyreason'of the fact that transmi. ion regulators for maintaining the transmission constant under different weather conditions will not be necessary.

. The curve D represents the variation of the attenuation with frequency under wet weather conditions where the pins and cross-arms have been short-circuited. It will be observed that the transmission loss due to the conductance G of Fig. '5 has been reduced to almost half i s original Value. The variation of the loss in pin and cross-arms duo tochanging weather conditions has likewise been eliminated. It will be understood, of course, that the loss may be further reduced by certain methods of insulator design which form no part of the present invention and need not be discussed herein.

In existing line construction, where wooden insulator pins are employed, the pins and cross-arms may be short-.circuited by metallic thimbles tied together in pairs by a metallic conductor, as shown. in Fig. 10, the thin bles being adapted to be slipped over the insulator pins, and the insulators then screwed into position. The thimbie may be formed by stamping it out of metal in the shape shown in Fig. 8, the main bodyof the thimble being stamped in the general form of a trapezoid, as shown at 25, with a circular member 26 integrally connected thereto at the upper margin to form. the top. of the thimble. Corrugations 27, are formed in the material, as shown in Figs. 8 and 9, so that when the two, side edges of the member are brought into juxtaposition and the top Inemher 26.bent down, as shown in Fig. 10, a screw-threaded thimble is formed which is, in effect, slotted along one side, as indicated at 28, so. that the thimble may be mounted upon theinsulator pin by simply springing it QYQ E the top thereof Without attempting to screw it into. place, i

Fig. 12 illustrates a standard form of wooden insulator pin which, it will he noted, is

' .thus mounted it locks the thirhbles. uponthe screw-threaded at the top so, thataiiiinsulator may be screwed upon it; The screw threads are. so shaped that-each thread. has a flat top nd he g oo ed P rti n. en djac n threads is substantially semi-circular, in the transverse section. In order to use'the thi n- I ble of the present invention, it isnecessary to Y so shape, the corrugations 27 of FigIS as to form a thread which will .co-operate with the threads in the supporting pin and also cooperate with similar threads. on theinterzor of an insulator, T h e corrugations 27 are,

therefore, not so formed as to. follow th'e external configuration of the threads on" the insulator pin but, on the contrary, the threads are so shapedthat not only are the spaces between adjacent threads semicircular in section but also the external surfaces of the threads themselves are also 03E semi-circular section. This is clearly indicated at 29 and :30 of Fig. 11.

\Vith this arrangement the part of the metal of the thimble'which forms the groove between adjacent threads conforms to the semi-circular groove between the threads on the. insulator pin. On the other hand, the insulator itself is formed with an interior screwihrcad, as indicated at 31 of Fig. 13, which is just the reverse of the type of thread shown upon the pin in Fig. 12, that is, the spaces between threads are flat and-the surfaces of the threads themselves are semicircular in section. If the internal thread of the insulator be made of slightly larger diameter than that of the standard insulator, it will be clear from Fig. 9 that the half-round threads of the insulator will ride between the half'round threads of thetliimble, and the projecting half-round surfaces of the thimble will project into the flattened space between the adjacent threads of the-insulator. This form of the thread in the thimbleenables threads of the standard shape to be employed in both the pin and the insulator.

As shown in Fig. 10,.the thimbles will be formed in pairs, tie pairs being joined together by a conductive strip 32. The thirnbles thcmsclres may be of copper, gilding metal, commercial bronze, or other suitable conducting m'etal, and similarly the conducting strip 32 may be formed of any well-known conducting material, although an annealed copper with its surface tinnedisfound preferable for this purpose. The conducting strip may beattached to'the thimblesby riveting, spot welding, soldering or thelike.

' In the useofthe device shown in Fig; 10,

where it-is desiredto short eircuit the orossarm wooden pins of a particular pair of conductors, the old insulators will be removed from the pins and the thimblessliown in Fig. 10 will then be sprung over the-threads of the wooden pins. New insulators, having .their' inner bore of enlarged diameter, will .thenbe screwed into place. When the. insulator-T .is

insulator ins and the: thimbles, -together with the conductor 32, effectively short-cit cuit both the; wooden insulator fpinslandithe cross-arm; so that a 'metallic conductor of substantially no resistance eirtends fr'orn the inner surface'of one ih'sulatorto an'sadjacent insulator."I"? -:;il.:.-

At transposition points a-slightly different conditionis encpuntje'redf suchpoints. the two insulator pins of a pair, instead of being arranged sideby side on the c'rosssa'rru so that both pinsa-re on thesaine horizontal plane, must bearra'nge'd so-that one is above the other. This is necessary in order that a pair of conductors which starts outon .the same horizontal lane from an adjacent pole may be translated into avertical plane at the transposition point, that is, givena-hzilftwist, the wires being'given a fiirthei halfi twist between the pole'atwhich the transposition takes place and the'next succeedingpole, so that thev'arrive atthe succeeding pole again in a horizontal plane but fullytrans posed in position. In order to accomplish these transpositions the construction shown in Fig. 15 is employed, where 35 is a wooden pin mounted upon' the cross-ar'nr36 in the usual manner. The corresponding pin is mounted upon a metal-"bracket 37 having a U-shaned member 38 which may be slipped over the cross-arm 36 and clamped thereto by means of a bolt 39. One leg of the U-shaped member is bent at right angles to form astep member 40.uponwhich is mounte'di aunetatlic' 1 pin 41,ithe metallic pin'being' clamped I'Dithef step member 40 by a nut The'pin llcarelies a 3 wooden coo-43,]upon which the g'in'sue latoristobesorewech n lnivie-w of the-peculiar:jmountingof. the insulator Supporting pinsjust described, it is not practicalstoyus'e t-Wo thimbles perma: nently 'connectedtogetheri at, transposition points and for such installations the type or thimble shownin Fig; 1 4 will beused, -As wili be apparent from ,F igi, 1 1;, the thimble proper is identical in structurewith ;tl1 at il-. iustrated in Fig. 10 but, instead ofbeing strapped through'a conductor to another thimble, thefthimbl'e shoWlI, in Fig. 14a is proided with a special conductor strip 44; which terminates at its opposite end in a bifurcated portion 45. One thimble of the type shown in Fig. 14 will then be sprung over the wood en pin 35 and the conducting strip will then be suitably bent over the cross-arm so that the bifurcated portion 45 may be clamped to the bracket 37 by means of the nut on the bolt 39. Similarly, another thimble of the same type will be sprung over the wooden cob 43, and its conducting strip 44 will be bent into such form that the bifurcated portion 45 may be clamped under the nut 4-2 which holds the metallic pin 41 in place. The insulators are then screwed into place over the two thimbics. It will be seen that a low resistance connection is established from the inner surface of one insulator, through the conducting strip 44, the bracket 37, and thence through the conducting strip 44, to the other insulator. In practice, thimbles of the type shown in Fig. 14- would be provided with conducting strips of different lengths so that the equipment could be accommodated to the requir ments of particular situations.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the following claims Vhat is claimed is:

1. In a pole line construction comprising a pair or" conductors strung along on poles with cross-arms carrying insulators mounted upon pins, one of said conductors acting as a return for the other, means to short-circuit the conductance of the cross-arm and its insulator pins between the insulators of the two wires of the pair comprising conductive thimbles of non-magnetic material prov ded with screw threads to co-onerate with the threads upon the pins, a conductive strip of non-magnetic material connected to each thimble for electrically connecting the thimble corresponding to one wire of the pair through a low resistance circuit to the thimble corresponding to the return wire of the pair, the insulators thimbles. .5 X In a pole; line constructio comprising a pairof conductorsstrung along on poles with ro -a a ryingins l te swa t d .9 P ne: .01 i l i c nt n nts; w s-e i turn for; the other, means. to; shor tc ircuit he; nductanqefiot the, cross-arm and t in: w r rinsbst e th iesul fio se t e t owires of the pair com'pris ing conductive fliimble s enmee e i nnt P id s i it; 0 U. 12ft ewes.- be 'sni'i gj nto p s i 1. thesu pOrting pinsQanda co id g'str p 0f mamas U "at l semen- ,1. tbf 'r' h thimble oi-electrically coiiiie c'ti'ng thethini ble corresponding to one wire of the pair to the thimble corresponding to the return wire of the pair.

3. In a pole line construction comprising a pair of conductors strung along on poles with cross-arms carrying insulators mounted upon pins, one of said conductors acting as a return for the other, means to short-circuit the conductance of the cross-arm and its insulator pins between the insulators of the two wires of the pair comprising pairs of conductive thimbles, the'thimbles of non-magnetic material of each pair being screw-threaded to co-operate with the screw threads upon the supporting pins and each thimble being split at one side so that it may be sprung into position with its threads in engagement with the threads of the supporting pins, the thimbles being connected together in pairs through a conductive strip of non-magnetic material whereby When a pair of thimbles is mounted upon a pair of pins and the insulators screwed upon thethimbles, a low resistance connection will be established from the interior surface of the insulator supporting one wire of the pair to the interior surface of the insulator supporting the return wire of the pair.

4. A thimble to be mounted upon an insulator pin of a transmission line, said thimble being formed of a biank having a single main body in the form or" a trapezoid and a circular projection at the top to form a cap, corrugations formed in the main body so that when the side edges of the main body are brought into juxtaposition the corrugations form threads in a split thimble-shaped member, the threads being of such pitch as to co-operate with the threads upon the insulator pin.

5. A thimble to be mounted upon an insulator pin of a transmission line, said thimble being formed of a blank having a main body the form of a trapezoid and a circular projection at the top to form a cap. corrugations formed in the main body so that when the side edges of the main body are brought into juxtaposition the corrugations form threads in a. split thiinble Shaped member, the threads being of such pitch as to cooperate with the threads upon the insulator pin and also being so forined as to lock the thimble in position upon the insulator supportingpin when an insuia'tor is screwed over the thin'ible.

6. An insulator mounting for a transmission line comprising a supporting pin upon a cross-arm, said-supporting pin having screw threads upon which an insulator may be rnounted, said'screw threads having flat outer surfaces with grooves between adjacent threads of substantially half-round section, a nietallic thimble adapted to be mounted on the supporting pin, said thimble having threads formed therein whose externally projecting surfaces are half-round in section and whose internally projecting surfaces are also half-round in section to co-operate with the half-round sections between the threads on the supporting pin, and an insulator provided with internal, half-roundscrcw threads to mate with the external screw threads upon the supporting pin, said screw threads being of somewhat larger diameter so that the insulator may be screwed upon the outside of the thiinble with the internal half-round threads engaging between the external halfround threads upon the thimble.

In testir'nony whereof, we have signed our names 'to this specification this 25th day of J une, 1925. r

CHESTER S. GORDON. JAMES T. LOWE. 

